Separation of isomeric mixtures of nitroanilines



Patented Mar. 2, 1954 SEPARATION OF ISOMERIC MIXTURES OF NITROANILINES Thomas W. Zbornik'and Dean J.

Slagle, Charles City, Iowa, assignors to Dr. Salsburys Laboratories, a corporation of Iowa No Drawing. Application December 14, 1951, Serial No. 261,926

8 Claims. (Cl. 260-582) This invention relates to a method of purifying nitroanilines;

Its more specific object is the separation of the mixed isomers of orthoand para-nitroanilines such as accrue in the ammonolysis of chloronitrobenzenes.

in the commercial preparation of orthoand para-nitroaniline chlorobenzene is first nitrated into the corresponding nitro product whereby a mixture of 65 per cent-para-chlcronitrobenzene and 35 per cent of its ortho isomer are formed. It has heretofore been common practice to separate the nitrated chlorobenzenes prior to 3111111131: tion in order to securev the ortho: and paranitroaniline in isolated and purified form. However, this procedure is inconvenient, uneconomical and unsafe. It is carriedout by aseries of alternate fractional distillations and crystallizations to obtain a gradual enrichment of the para portion in the first fractions and of the ortho isomer in the final distillates. one of the main diificulties of this process resides in the fact that the boiling points of the two isomers are only 6 apart from each other. This necessitates repeated distillations and crystallizations, is a time consuming process and requires a considerablecapitalexpenditurefor equipment. Moreover, many industries hesitate to embarkupon this project on account of the serious toxicity hazards involved by this procedure, particularly during the summer season.

"It is therefore an object of the present invention to devise a method of producingorthoand para-nitroaniline in isolated state without resorting to the tedious and expensive separation of its chlorinated precursors.

* It is a second object of the present invention to produce the isomers in and without sensible losses in raw materials or reacting agents.

Still another object of the present invention is to design a process for the preparation of orthoand para-nitroaniline in isolated form which is simple and inexpensive in operation and ensures excellent yields of each constituent of the isomeric mixture. 1

Other benefits and. advantages of the invention will appear from the following description and examples, it being understood, however, that these are not limitative of the scope of the invention, but only illustrative embodiments thereof.

We havefound that the necessity of separating. isomeric chloronitrobenzenes can be eliminated by a simple and efiicient treatment of g the aminated derivatives by which the isolation oia high degree of purity the paraand ortho-nitroaniline is accom-= plished. Previous efforts in this direction have resorted to the use of caustic alkali solutions which have been found to possess a selective solvent power for the ortho-isomers 'within' certain elevated temperature limits. t must be considered, however, that the handlin of large volumes of hot caustic liquids entails'a great deal of inconvenience, hazards, and deterioration due to the corrosive action of the alkalinesolutions. Furthermore the effective temperature range of selectivity is confined Within relatively narrow limits which are difiicult to maintain in commercial operations. Consequently a sharp separation cannot be obtained which makesit impossible to recover pure ortho nitroaniline.

Our new and improved method overcomes these difficulties and shortcomings by making use of the differences in solubility of, the two isomeric nitroanilines in various organic solvents and the preferentialafiinity of acids-for the para nitroaniline in the formation of solid salts while the ortho compound remains in solution.

In greater detail, the starting material in our process is a commercial mixture of nitroanilines comprising about of the para derivative and 35% of the ortho isomer. It should be noted, however, that this proportion of isomers ismerely illustrative and in no way a critical limitation of thisinvention, and the composition may of course vary with the source and mode ofpreparation of the original compounds. Whenthe mixture of the isomers is treated with an organic solvent, such as carbontetrachloride, under suit. able conditions, all of the ortho nitroaniline will go into solution while most-of the para isomer remains as an insoluble residue. It has, however, been observed that during this operation with rising concentrations of the ortho compoundin the solvent the same loses its selectivity and that consequently appreciable amounts of the para derivative are drawn into the ortho nitroaniline solution. These portions of the valuable para compound would be lost from the yield and, moreover, the ortho isomer Would not be obtained in purified form, if the separation were to stop short at this stage. After the filtration of the major part'of the pure para nitroaniline the filtrate is therefore subjected to a second; treatment which will separate the ortho derivative from the associated para fraction. Since no fractional crystallization will yield from this mixture a pure ortho nitroaniline, a different process is applied to produce the desired result.

We have found that if the filtrate is treated with an acid, the para nitroaniline will preferentially be bound by it in form of a solid salt. Thus, if a stream of anhydrous hydrogen chloride is bubbled into the carbontetrachloride solution containing substantiallyall themrtho mitroaniline and a smalLproportiomof its para isomer, all. of the para compound precipitates out in form of its hydrochloride along with some ortho nitroganiline hydrochloride. The solid salts may be either discarded or filtered off; washed with asmall amount of organic solvent, neurtalized with an alkaline agent and returnedito; a: starting batch for recycling. The filtraternow contains pure ortho nitroaniline which is recovered by any conventional means sucln as. cooling or evaporation. It has been determined" that :.-the;. purity of the resulting ortho isomer largely depends upon the amount of acid addeditdthe filtrate. As a preferable, though not limitative 2 modmof operation.-..itz-zhasrzbeen.found. that anexcessf-overr. stoichiometric.- amount. requiredfor. tries-neutralization. of, the parascompound-should hoiusede in. order. to assurerthatl all of, the. para. nitrcanilinef-ise precipitated. Thesolyentmay; he recovered in; any convenient-mannen.

The following examples: will; further. describe. the -preferred eml:udimentsI oi. our. invention. by, war; of: illustration.-. All that parts-.referred; to. ares-torbe -understood-.as 'partsvby weight- Example-.1-

o'ne -hundred part's of aimixture containingzfih: percent of 'para nitroanilineaand 35 pencent'of: ortho nitroarriline are' mixed with 240Z1parts: of; carbontetracliloride; and 'thev solution is*-. heated: to about 55-'G". for approximately" ten minutes. The solidportionof the pure parannitroanilinezis then filtered ofi' and' washed w-itii fifliparts ofxcare bemtetraclilbridd at a temperature oft-55 6: A stream=-of anhydrous hydrogen: chloride is then introduced int'o the filtrate= at: 55 G; with con:- stant agitation; 'l he precipitate of isomeric:ni troaniline hydrochlorides is filtered ofi, washed with 30 parts of caa'bontetrachloride which is lieated t'o-about 55 and-neutralized with a solution'of sodium hydroxide; it: contains a mixtime of ortho -and-* para-nitroanilines: which: is returned-to-an'or-iginal batchifon recycling; The carbontetrachloride solution-now containing pure orthonitroanili'ne is" cooled down to about- 0 C? and the" crystalline -precipitate is filtered off'and dried. The-yields-obtained are-asdolloWsr Parts Eara -nitroaniline- E=l65 to 1475' Ortho-nitroaniline- (Ma' R570 0: 1:0"1115' C;) 3r Eecycle-nitroanilines 6 Unaccountedffor loss- 1' Example 2' Thee. isomeric. mixtures of. nitroanilines. is. treated iii-the same. manner: as .in.Example. 1, ex-.- ceptsthatinstead ofihydrogemchloride, five-parts Ofi'-9&.'; 07=Sl11f.\1!i(3- acid are. used. tor theprecipitaa tiomoi. the.-salt. mixture.- containing ortho nitroaniline. and. a small. amountof. its. para isomer. The nitroaniline sulfate are filtered. ofi, washed with-: parts, of carbontetrachloride. and .neutralized. with. a. solution of. sodium hydroxide to, berecycled. The carbontetrachloride solution cooledmoi C.-.andmhaonthdmtmaniline crystals. 7s. 0 .'benzene.heldatg-atenmerature.ofidil ci.

4 are filtered off and dried. The yields obtained are as follows:

Parts Para nitroaniline (M. P.=l46 C. to 147 C.) 62 Ortho nitroaniline (M. P.= C. to 71 C.) 29 Rzec'yclea'nit-roanilines 7 Unaccounted for-.loss 2 Example 3 Thissexperiment follows the steps in Example 1, with the exceptiodthat before the addition of carbontetrachlorideto the starting mixture of .theeisomersdmliparts of water are added. After filtration of'th'e pure para nitroaniline the water layerris decantedand anhydrous hydrogen chloride introduced. The separation is thereupon completed.-.as in the foregoing runs and the yields 0 obtained are as follows:

The=procedure is tl'ie same as in Examplel, ear cept" that the acid treatment: is:penh'armevzi 9- parts of para phenolsulfonic acid which are added t0- the first filtratea 'I he =yiellis'obtained areas follows:

Farts Para-nitroaniline-(M?P7=146G. to-lWCJ's 62 Ortho nitroaaiiiine=(M Gt to 7? C1) 29 Recycle nitroanilines--- 'T. Unaccounted Tor loss; 2

Exempted One; hundred; fifty parts-toi a; wet-.- mixturesof: orthorandipara-nitroanilinea containinggfifi (pen cent: water are. addedi with :parts carbon'e tetrachlorideheated to about.;:5&? and the solution:isrthemfiltereda The remaininec'sclids are resuspended in a sceondtportinnmiz Bib-Eartha of carbcntetrachloridw. held;.at 55% G. for: about 10; minutes; and: filteredgoffi. hQi'W'Q IZQE layflzisthereupon; decanted; from the; filtrate and the carbontetrachloride; solution: is: combinedii with the first filtrate of theqcrudez onthueisomerr and the; solution: is; subsequently; treated-.- with anhydrous;hydrogenzchlorideandatherprocessloitsepas ration completed as in: Rambler-.1; Theirielsls. obtained are as follows:

Rant EaraanitroanilineAM. B-J=ll5= 0,; to. M13" (3?) a. .1 Qrtho nitroaniline (M2.B=68;52: Gr. to,-70;5?

CD; ......m i-.. s- 28: Recycleinitroanilines M. 8) Unaccounted for loss--- 3:

Exempted 7 L0.0..-parts.oizamixturecomainingfittner center.

para nitroaniline and'35per cent of its ortho isor. mer. are. mixed.- with. 20.0. parts of. benzene. and heatedat. 59. C... for. about. 15. minutes... The: solids are.- filtered; off; and washed with, 50" parts:

filtrate is thoroughly stirred and kept at a temperature of 55 C. while anhydrous hydrogen chloride is introduced into the solution. After the precipitate of nitroaniline hydrogen chlorides is formed, the same is collected on a filter, washed with 50 parts of warm benzene and neutralized with a solution of sodium hydroxide. The mixture of ntroanilines is filtered and recycled. The benzene filtrate is evaporated and the pure ortho nitroaniline crystals are recovered therefrom and dried. The yields obtained are as follows:

Parts Para nitroaniline (M. P.=144 C. to 146.5"

C.) 56 Ortho nitroaniline (M. P.=66 C. to 68 C.) 26 Recycle nitroanilines 16 Unaccounted for loss 2 It should be noted that the above outlined procedure of separating mixed isomers of ortho and para-nitroaniline is independent of the source and physical condition of the starting material. It is applicable regardless of the form in which the mixture is provided, whether it be a wet filter cake originating from the ammonolysis of chloronitrobenzene, or a dry powder, or a solid solution, or a melt.

Likewise our new method shall not be confined to the specific solvents shown in the foregoing examples. Practically every organic agent in which the ortho isomer is preferentially soluble may be used, and in addition to those mentioned in the examples the following will serve the purpose desired: chloroform, ethylene dichloride, 1,1.2-trichloroethane, trichloroethylene, benzene, toluene, and xylene. Carbontetrachloride is a conventional solvent as it is inexpensive, noninflammable and well suited for plant operations.

It may of course, be necessary to adjust the temperatures and other operating conditions in accordance with the boiling points and varying physical characteristics of the solvent employed, and any such modification as required by the nature of the separating agent will readily occur to a chemist skilled in the art. Thus, if a low boiling solvent is used, it might be advisable to carry out the solution in a reflux condenser. In the event that the solvent has a relatively high boiling point, such as benzene or para xylene, it will be preferable to recover the ortho nitroaniline from the solution by evaporation or distillation instead of refrigerative crystallization. Again in certain cases it may be desirable to use a mixture of two or more solvents to lower the boiling point of the dissolving medium.

Although for the purpose of isolating the pure ortho nitroaniline from the organic mother fll trate the examples suggest the use of anhydrous hydrochloride, hydrochloric acid, sulfuric acid and para phenolsulfonic acid, it will be understood that many other organic and inorganic acids may be employed to the same effect. Additional examples are nitric acid, phosphoric acid, arsenic acid, benzene sulfonic acid and toluenesulfonic acid. One of our preferred embodiments is the precipitation of para nitroaniline by anhydrous hydrogen chloride, as this is an inexpensive agent which readily disperses in the stirred filtrate and gives sharp separations. The term hydrogen chloride as used in the claims shall be understood to include both the anhydrous and the aqueous form.

While the invention has been described in accordance with our preferred embodiments, it will be apparent that numerous variations and modifications may be resorted to without departing from the spirit of the invention and that all these shall be included as equivalents within the purview of our invention as defined in the followin claims. What we claim is:

1. The method of separating mixed isomers of orthoand para-nitroaniline which comprises the steps of subjecting the isomeric mixture to the action of an organic dissolving medium of sub stantially selective affinity for the ortho isomer selected from the group consisting of carbontetrachloride, benzene, toluene, xylene, chloroform, ethylene dichloride, 1,1,2, trichloroethane, and trichloroethylene separating the undissolved para nitroaniline from the solution, treating the solution with an acid selected from the group consisting of anhydrous hydrogen chloride, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, arsenic acid, benzene sulphonic acid, toluene sulphonic acid, and paraphenol sulphonic acid to form an insoluble para nitroaniline acid salt, separating said insoluble acid salt of para nitroaniline from the ortho isomer solution, and recovering the ortho nitroaniline in the remaining liquid.

2. The method of separating mixed isomers of orthoand para-nitroanilines which comprises the steps of subjecting the isomeric mixture to the action of carbontetrachloride, separating the undissolved para nitroaniline from the solution, treating the solution with hydrogen chloride, separating the undissolved para nitroaniline hydrochloride from the ortho isomer solution and recovering therefrom the ortho nitroaniline.

3. The method of separating mixed isomers of orthoand paranitroaniline which comprises the steps of subjecting the isomeric mixture to the action of carbontetrachloride, separating the undissolved para-nitroaniline from the solution, treating the solution with sulfuric acid, separating the undissolved paranitroaniline sulphate from the ortho isomer solution, and recovering therefrom the ortho nitroaniline.

4. The method of separating mixed isomers of orthoand paranitroaniline which comprises the steps of subjecting the isomeric mixture to the action of carbontetrachloride, separating the undissolved para-nitroaniline from the solution, treating the solution with para-phenolsulphonic acid, separating the undissolved paranitroaniline para-phenolsulphonate from the ortho isomer solution, and recovering therefrom the ortho nitroaniline.

5. The method of separating mixed isomers of orthoand paranitroaniline, which comprises the steps of subjecting the isomeric mixture to the action of benzene, separating the undissolved paranitroaniline from the solution, treating the solution with hydrogen chloride, separating the undissolved paranitroaniline hydrochloride from the ortho isomer solution and recovering therefrom the ortho nitroaniline.

6. The method of separating mixed isomers of orthoand paranitroaniline, which comprises the steps of subjecting the isomeric mixture to the action of ethylenedichloride, separating the undissolved paranitroaniline from the solution, treating the solution with hydrogen chloride, separating the undissolved paranitroaniline hydrochloride from the ortho isomer solution, and recovering thereform the ortho nitroaniline.

7. The method of separating mixed isomers of orthe- :anci- @arasnitroani-lines which comp ises thessteps of zsubjeetingmvwet. isomeric mixture to the-section :ofrwarmiea bontetrachloride, separat ingnthe nmiissolved- ,paranitro'aniline'firom the solution, mesuspending the solid para isomer .in avenm carbontetraehloride; ancl'filterlng the same from the suspending agent, decanting the water layer from the predominantlyortho isomer. solution; combining it with the first ortho-isomer solution treating; thecembmedsolutions withhyudrogemchloride, separating the nndissolved para. nitroaniline hydrochloride from the liquid, and 'reeoveringv therefrom pure 'ortho i-nitroaniline;

18;. The, method of separating mixed isomers of ,anthoanti para'nitroanilinewhich comprises the steps. "of subjecting. the isomeric mixture to the nation of an erganie dissolving medium of substantially selective afiinity for the ortho-isomer selected fromthe-group consisting :of carbon- .tetraehleride, benzene, toluene, xylene, .chlono- 20 iorm. ethylene dichloride, -1;,1,2-trichloroethane, and": trishloroethylene separating the undissolved paiza-nitroaniline from the solution, treating the solution with an acid selected item the :group consisting of anyhdrous hydrogenehloride, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, arsenic acid, benzene sulphonic acid, toluene sulphonic acid, and paraphenol sulphonlc acid.- to-form an insoluble said salt of. predominantly para-nitroaniline, separating said acid saltfromfthe solution, washing :and neutralizing :the separated solid, returning the same "to-the starting mixture of the isomers, and recovering the ortho-nitroaniline from the remaining liquid.

THOMAS W. Z'BORNI'K, DEAN J. SLAGLE.

References Cited in the file of thispatent UNITED STATES PATENTS Number Name Date 2,128,699 Frye Aug. 30;. 1938 2,408,975 Engel A..- Oct. 8,1946 

8. THE METHOD OF SEPARATING MIXED ISOMERS OF ORTHO- AND PARANITROANILINE WHICH COMPRISES THE STEPS OF SUBJECTING THE ISOMERIC MIXTURE TO THE ACTION OF AN ORGANIC DISSOLVING MEDIUM OF SUBSTANTIALLY SELECTIVE AFFINITY FOR THE ORTHO-ISOMER SELECTED FROM THE GROUP CONSISTING OF CARBONTETRACHLORIDE, BENZENE, TOLUENE, XYLENE, CARBONFORM, ETHYLENE DICHLORIDE, 1,1,2-TRICHLOROETHANE, AND TRICHLOROETHYLENE SEPARATING THE UNDISSOLVED PARA-NITROANILINE FROM THE SOLUTION, TREATING THE SOLUTION WITH AN ACID SELECTED FROM THE GROUP CONSISTING OF ANYHDROUS HYDROGEN CHLORIDE, HYDROCHLORIC ACID, SULFURIC ACID, NITRIC ACID, PHOSPHORIC ACID, ARSENIC ACID, BENZENE SULPHONIC AICD, TOLUENE SULPHONIC ACID, AND PARAPHENOL SULPHONIC ACID TO FORM AN INSOLUBLE ACID SALT OF PREDOMINANTLY PRAR-NITROANILINE, SEPARATING SAID ACID SALT FROM THE SOLUTION WASHING NAD NEUTRALIZING THE SEPARATED SOLID, RETURNING THE SAME TO THE STARTING MIXTURE OF THE ISOMERS, AND RECOVERING THE ORTHO-NITROANILIME FROM THE REMAINING LIQUID. 